During some semiconductor manufacturing processes, electrical charge can be stored on the wafer. For example, during plasma etching, reactive ions are generated in an ion discharge chamber and accelerated by an electric field. These ions collect on the wafer surface, accumulating in, for example, circuit elements on the substrate such as p-type and n-type doped well. The statically stored charge in the wells can ultimately discharge, potentially damaging the devices. Antenna diodes are used to dissipate the charge stored in the wells to avoid damaging the devices. The stored charge is dissipated to, for example, the substrate.
FIGS. 1a-b show one implementation of a conventional n-well antenna diode 100. Referring to FIG. 1a, a p-type substrate 101 having an n-well 110 is shown. A first terminal 120 is coupled to the n-well using a heavily doped n-type diffusion region 115; a second terminal 125 is coupled to the substrate using a heavily doped p-type diffusion region 105. The first terminal is coupled to a high potential (e.g., VDD) while the second terminal is coupled to a low potential (e.g., ground). A diode 140 is coupled between the first and second terminals, with the anode being coupled to the second terminal and the cathode being coupled to the first terminal. The diode 140 can be realized by, for example, forming a heavily doped p-type diffusion region 142 in the n-well and coupling it to the second terminal 125, as shown in FIG. 1b. 
Coupled between the first and second terminals is an over-voltage protection circuit 130. The over-voltage protection circuit serves to suppress EOS, such as electrostatic discharge (ESD) from damaging the IC. FIG. 1c shows an ESD current path 151. In normal operation, the second terminal is at a lower potential than the first terminal. However, during an EOS event, a spike (e.g., overstress voltage) at the second terminal causes it to have a higher potential than the first terminal. This causes the ESD current to flow from the second terminal to the first terminal through the over-voltage protection circuit.
The invention relates to improved antenna diodes for dissipating statically stored charges in ICs.